The present invention relates to a seat reclining device for a vehicle, adapted to adjustably fix an angle of a seat back relative to a seat cushion.
As a vehicle seat reclining device, there is a device which is constituted by a body frame mounted to a base plate on a seat-cushion side and a cover member mounted to an arm plate on a seat back side, and which is arranged to limit a relative rotation between the body frame and the cover member and to maintain a desired angular position of the seat back by engaging an external gear of a lock tooth attached to the body frame with an internal gear formed in an inner peripheral surface of the cover member.
In order to fix the lock tooth, the body frame is formed with a shaft portion and a pair of guide projections in the vicinity of the internal gear. The lock tooth has a concave bearing surface which is guided by a convex guiding surface of the shaft portion, and a sliding surface which is slidably in contact with a concave guiding surface of the guide projection. Moreover, a cam for pressing the lock tooth to the outer side so as to engage the external gear with the internal gear is provided at a rotational-center portion of the internal gear.
In thus-arranged seat reclining device, at the time of vehicle rear collision, the lock tooth receives an external force of rotating the seat back in the backward direction through the engagement between the internal gear and the external gear. At this moment, since the lock tooth is supported by the shaft portion and one of the pair of guide projections, the rotation of the cover member relative to the body frame is limited, and therefore the seat back is not rotated from a predetermined angular position.
Although a belt anchor for supporting a force applied to an upper portion of seat belt is conventionally provided at a center pillar of a vehicle body, there has been lately increased a type that the belt anchor is provided at the seat back. Therefore, in the case of the belt anchor provided at the seat back; an inertia force due to a weight of a vehicle occupant during vehicle collision is transmitted to the seat back through the seat belt, and hence a force greater than that of a type that the belt anchor is provided at the center pillar is applied to the seat back in the forward direction. Accordingly, the vehicle seat reclining device of the type that the belt anchor is provided at the seat back is lately requested to be durable to a further large load.
Japanese Patent Application Publication No. 2004-16651 discloses a previously-proposed seat reclining device for vehicle. In this technique, three pawls disposed at circumferentially even intervals are guided so as to be radially movable along respective guide grooves of a lower arm. Two parallel surfaces of a rotating shaft are loosely fitted into a center hole of a cam, and three projections provided to the cam at circumferentially even intervals are loosely fitted into corresponding cam holes of the three pawls. When rotating the rotating shaft; each pawl moves in a radially outward direction, and an outer gear of each pawl is engaged with an inner gear of an upper arm so that the upper arm is locked relative to the lower arm.